Directional audio systems work by spatially filtering received sound so that sounds arriving from the look direction are accepted (constructively combined) and sounds arriving from other directions are rejected (destructively combined). Effective capture of sound coming from a particular spatial location or direction is a classic but difficult audio engineering problem. One means of accomplishing this is by use of a directional microphone array. It is well known by all persons skilled in the art that a collection of microphones can be treated together as an array of sensors whose outputs can be combined in engineered ways to spatially filter the diffuse (i.e. ambient or non-directional) and directional sound at the particular location of the array over time.
The prior art includes many examples of directional microphone array audio systems mounted as on-the-ear or in-the-ear hearing aids, eye glasses, head bands, and necklaces that sought to allow individuals with single-sided deafness or other particular hearing impairments to understand and participate in conversations in noisy environments. Among the devices proposed in the prior art is known as a cross-aid device. This device consists basically of a subminiature microphone located on the user's deaf side, with the amplified sound carried to the good ear. However, this device is ineffective when significant ambient or multi-directional noise is present. Other efforts in the prior art have been largely directed to the use of moving, rotatable conduits that can be turned in the direction that the listener wishes to emphasize (see e.g. U.S. Pat. No. 3,983,336). Alternatively, efforts have also been made in using movable plates and grills to change the acoustic resistance and thus the directive effect of a directional hearing aid (see e.g. U.S. Pat. No. 3,876,843 to Moen). Efforts have been made to increase directional properties, see U.S. Pat. No. 4,751,738 to Widrow and Bradley, and U.S. Pat. No. 5,737,430 to Widrow; however, these efforts display shortcomings in the categories of awkward or uncomfortable mounting of the microphone array and associated electronics on the person, hyper-directionality, ineffective directionality, inconsistent performance across sound frequencies, inordinate hardware and software complexity, and the like.
All of these prior devices allow in too much ambient and directional noise, instead of being focused more tightly on the desired sound source(s) and significantly reducing all off-axis sounds. This is largely due to their having beam widths so wide and side lobes so large that they captured much more than the desired sound source(s). In contrast, highly directional devices must have beam widths less than or equal to 25 degrees. In addition, prior art devices have had beam widths which varied significantly over frequency (making accurate steering more demanding) and lacked sufficient directivity gain due to the small number of microphones employed in general, and the limited effective aperture of the array.
As a result of these deficiencies, commercialized hearing aids, even augmented with prior microphone array technology, are considered ineffective by a majority of users in noisy and reverberant environments, such as restaurants, cocktail parties, and sporting events. What is needed, therefore, is a wearable directional microphone array capable of effectively filtering ambient and directional noise, while being comfortably and discreetly mounted on the user.